Preparation of chitosan-stabilized Fe(0) nanoparticles for removal of hexavalent chromium in water.

Chitosan-stabilized Fe(0) nanoparticles (CTO-Fe(0)) and Fe(0) nanoparticles synthesized in ethanol-water mixed system (EW-Fe(0)) were tested for reduction of Cr(VI) in water. Fourier transform infrared (FTIR) study suggested that nitrogen and oxygen atoms are the binding sites for chitosan on iron which was accountable for the stability of Fe(0) nanoparticles. While the EW-Fe(0) ignites spontaneously when exposed to air, the CTO-Fe(0) was still in zero valence state after exposure to air over 2-month period as shown by X-ray powder diffraction patterns. Batch experiments demonstrated that the maximum Cr(VI) reduction rates for CTO-Fe(0) was about 3 times higher than EW-Fe(0). Characterizations with high-resolution X-ray photoelectron spectroscopy (HR-XPS) revealed that Cr(VI) was reduced to Cr(III) and Fe(III) was the only component present on the Fe(0) nanoparticles surface. Additionally, chitosan can inhibited the formation of Fe(III)-Cr(III) precipitation due to its high ability to chelate Fe(III) which resulted in k(obs) for CTO-Fe(0) was about 1-3 times higher than EW-Fe(0). Due to the fast reaction kinetics and good stability against oxidation in air, the chitosan-stabilized Fe(0) nanoparticles have the potential to become an effective agent for in situ subsurface environment remediation.